GENEVA (Reuters) -An Israeli incursion in Rafah would put the lives of hundreds of thousands of Gazans at risk and be a huge blow to the aid operations of the entire enclave, the U.N. humanitarian office said on Friday, as the World Health Organization announced contingency plans for an incursion. Israel has repeatedly warned of an operation against Hamas in the southern Gazan city of Rafah, where around a million displaced people are crowded together, having fled months of Israeli bombardments triggered by Hamas fighters' deadly cross-border attack on Oct. 7.